Vaughn hails from the University of Mississippi, where he was teammates with Lions linebacker Ashlee Palmer. He was signed by Denver as an undrafted free agent in 2010 and played two seasons there.

He started 15 games in past two seasons for the Colts, and had a career-best three interceptions in 2013. He ranked 76th at the position last season, according to ProFootballFocus.

That's not very good, though it was better than both of Detroit's starters, Darius Slay (92nd) and Chris Houston (96th).

Slay and Houston are back this year and currently projected as the starters. Bill Bentley returns as the team's primary nickel man, while Chris Greenwood and Jonte Green are under contract as reserves.

The Lions are looking for upgrades, though, after finishing in the bottom third of the NFL last year in pass defense.

Mathis remains an option as well. He didn't sign until the middle of training camp last year, and turned out to be Detroit's best corner. The 33-year-old veteran could follow a similar trajectory this year if the Lions strike out elsewhere.